A gas sensor with a heated gas-sensitive semiconductor element as the measuring element is known, for example, from DE 38 10 409 A1. One essential drawback of this prior-art arrangement is the poorer diffusion of the gas to be measured compared to the prior-art arrangements with support wires and catalytic measuring elements arranged thereon, i.e., especially to heat tone sensors called pellistors. The jacketing of the measuring elements represents an additional diffusion barrier. The gas-sensitive semiconductor elements or heat tone detector elements used to measure the concentrations of combustible or explosive and usually also toxic gases, vapors or gas mixtures contain hot components such as pellistors, whose hot surfaces may ignite an explosive gas mixture or gas-air mixture under operating conditions or in case of a defect. To avoid such life-threatening ignitions, which trigger explosions, by hot surfaces in the gas sensor, such sensors are designed with the “pressure-proof housing” type of protection according to the IEC/EN 60079-1 standard specification.
This means that, on the one hand, the power consumption of such sensors is limited by the actuating electronics thereof, so that the maximum surface temperature of the sensor housing is limited to a certain value.
On the other hand, a flame trap, which is integrated in the sensor housing and which is also used at the same time as a breathing means for the necessary entry of the gas or gases to be measured and the removal of the combustion products formed from the gas sensor, prevents the flame from spreading because of an ignition at hot measuring elements from the sensor housing. Even though the gas sensors, which are designed only according to the “pressure-proof housing” type of protection, may be used in areas in which a hazardous explosive atmosphere may be expected to be occasionally present, they may not be used in areas in which a hazardous explosive atmosphere is present continuously or for a long time.